Huge +1 from me as well. In its current state, police officers own the entirety of the justice system. This not only induces corruption and disparate punishments, but it's also discouraging to players that are punished for crimes that they may not have committed. Let's say, for example... a friend lends his car to another friend for the night without "giving him the keys" and a cop ends up pulling him over. In its current state, the borrowing friend is punished without trial for Grand Theft Auto without regard for the situation or the ability to defend himself and/or call upon a witness to prove the lawful transaction. It's unfair and unrealistic; just one example of many that could portray the message and why I +1 this.
All of the hurdles that people have brought up in this thread I agree with. Mainly, that the realistic justice system is slow and that capacity to have people available at needed times would be difficult. I think at least just considering the points brought up by original poster (e.g. police still able to prosecute as done today, only initiates DOJ involvement upon request for representation/in dispute of a crime, limited DOJ positions, etc.) would be a really cool addition to the server that could positively enhance the roleplay and player experience. I also want to add to this original suggestion to allow for private representation (law firms) as well as requiring all PD use dash and body cams (not sure if something like this is already a thing) for the purpose of prosecution & defense in the case of a potential trial.
I hope that this will get considered at some point!